[ODE] Hinge2 suspension

[Henry]

First off I'd like to say how great I think ODE is. I have practically 
no physics programming knowledge and it has taken me 2 days to get a 
pretty convincing car working. Thanks Russell for a great tool.

I've built my car using Hinge-2 to connect the wheels to the body. When 
i drop the car from 3 feet (don't ask) the suspension compresses nicely 
and rebounds realistically. The question I've got is how do i set 
suspension stops on axis 1? At the moment the wheels punch through the 
guards.

tia

henry